1. Field of the Invention
The present invention relates to a lens barrel of an imaging device. More particularly, the present invention relates to a lens barrel which includes a light blocking member that is provided so as to cover a peripheral part of a lens for blocking unwanted light rays traveling toward the lens.
2. Description of the Related Art
Optical devices, such as still cameras, focus light rays coming into a lens barrel using lenses and photograph an image of the converged light rays using a film or imaging element. However, inside the lens barrel, there are unwanted light rays which are not necessary for photographing, for example, light rays which are reflected inside the lens barrel to reach the lenses, as well as light rays necessary for photographing. When unwanted light rays reach a film or imaging element, a photographed subject image results in a ghost or flare image. Therefore, it is necessary to block such unwanted light rays so as not to enter the lenses.
A conventional lens barrel is described with reference to FIG. 7.
FIG. 7 is a partially enlarged view of a conventional lens barrel 100. The lens barrel 100 is provided with a lens 102, which is adhesively attached to the inner wall of the lens barrel 100. Light traveling inside the lens barrel 100 toward the lens 102 includes an effective light ray 104 which is necessary for photographing and an unwanted light ray 105. A light blocking member 103 is provided so as to cover a peripheral part of the lens 102 such that the unwanted light ray 105 traveling toward the lens 102 is blocked.
Japanese Laid-Open Patent Publication No. 2009-116085 discloses the technique of blocking unwanted light rays by providing a light blocking plate over some of the components provided inside the lens barrel (for example, FIGS. 4 and 5).
In the conventional lens barrel 100 shown in FIG. 7, the light blocking member 103 is usually formed by molding of a resin which is composed of a thermoplastic resin, such as ABS (Acrylonitrile-Butadiene-Styrene resin), and carbon black added thereto. An inner rim 103a of the light blocking member 103 need to be tapered at an acute angle in order to prevent generation of flare due to diffuse reflection of the unwanted light ray 105.
FIG. 8 is a schematic cross-sectional view of the inner rim of the conventional light blocking member 103. The light blocking member 103 is constituted of the main material 107 of a resin, such as ABS, and carbon black 108 added thereto.
As shown in FIG. 8, unwanted light rays 105 are reflected by the surface of the light blocking member 103 to enter the lens 102. In some cases, unwanted light rays 105 coming into the gap between the lens 102 and the light blocking member 103 are first reflected by the surface of the lens 102 and then reflected by the surface of the light blocking member 103 to enter the lens 102.
Now, we focus on the extreme edge 103b of the light blocking member 103. For production reasons, the extreme edge 103b is not perfectly an acute angle but has, in actuality, a spherical surface with the radius of curvature of about 0.01 (R≈0.01). Therefore, the unwanted light rays 105 reflected by the extreme edge 103b undesirably enter the lens 102 in many cases. As a result, the unwanted light rays 105 cause optical problems, such as flare and ghost. This means that such an optical problem still remains unsolved even though the light blocking member 103 is provided.